Purines, electron-donor properties

No detailed evaluation of the different factors contributing to this binding has been made yet. One quantitative relationship relevant to the binding has nevertheless been obtained. Thus we have been able to show that the solvent power of a series of purines toward, say, a given hydrocarbon runs parallel to the electron donor properties of the purines, as measured by the value of the energy coefficient of their highest filled molecular orbital. These values are reproduced in Table I for the essential biochemical purines and... 

TABLE I. Electron Donor Properties of Purine and Pyrimidine Bases... 

R is an electron-donor substrate such as purine or xanthine and A is an electron acceptor such as 02 or NAD+. It is thought that the in vivo mammalian form of xanthine oxidase uses NAD+ as acceptor and is therefore, more appropriately named xanthine dehydrogenase. No evidence exists for a dehydrogenase form of aldehyde oxidase. The specificities of xanthine oxidase and aldehyde oxidase have been extensively catalogued (96), and the mechanism and properties of these enzymes have been reviewed (97, 98). 

As noted for heteroatom attachment in 8-oxo-dG and C8-arylamine adducts, attachment of the Ph moiety to the C-8 site of dG enhances the one-electron donor characteristics of the purine nucleoside. The redox properties of 8-/>-X-Ph-dG (X = OH, OCH3, CH3, H, CN, CHO) adducts have been studied by cyclic voltammetry in anhydrous DMF. The C8-aryl adducts exhibited irreversible one-electron oxidation peaks with half-peak potentials ( p/2) ranging from 0.85 V versus saturated calomel electrode (SCE) for 8-/>-PhOH-dG (X = OH) up to 1.11 V/SCE for 8- -CHO-Ph-dG. All adducts were oxidized more readily than dG, which gave p/2= 1.14 V/SCE in DMF (Table 2). 

Electron-donor and -acceptor properties of biologically important purines,... 

Further studies of the deoxygenation of alcohols by triplet sensitisation and SET to their S-methyl dithiocarbonates under a variety of conditions have been reported. The properties of 2,4,6-triphenylthiapyrilium tetrafluoroborate as an SET sensitiser have been discussed. The triplet excited state of 6H-purine-6-thione acts as an electron donor for p-dinitrobenzene and as an electron acceptor for tetramethylbenzidine. Photolysis of sulfuryl chloride in the presence of tetramethylsilane yields exclusively Me3SiCH2S02Cl. In the presence of added yttrium(III) chloride or sulfur, the reaction is less selective and Me3SiCH2Cl is also obtained. In contrast the presence of these photocatalysts in the photoreaction of sulfuryl chloride with hexamethyldisiloxane yields solely Me3SiOSi-Me2CH2S02Cl, whereas in their absence Me3SiOSiMe2CH2Cl is also obtained. ... 

Very recently, these predictions concerning the electron-donor or-acceptor properties of different biomolecules have received a number of striking although sometimes indirect confirmations. This is in particular the case with the electron-donor or -acceptor properties of purines and pyrimidines. Thus, as already noted, these last types of molecule may be considered as... 

Pulhnan, B. and Pullman, A. (1958). Electron-donor and -acceptor properties of biologically important purines, pyrimidines, pteridines, flavins, and aromatic amino acids. Proc. Natl. Acad. Sci.USA, 44, 1197-1202. 

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